Method and apparatus for mitigating interference in a wireless communication system

ABSTRACT

Techniques to mitigate inter-cell interference using joint time and frequency division are described. A frequency band is divided into multiple non-overlapping frequency subbands. The transmission timeline is divided into T in  and T out  time intervals. Data is exchanged with users in at least one inner region of a cell on the entire frequency band in the T in  time intervals. Data is exchanged with users in multiple outer regions of the cell on the multiple frequency subbands in the T out  time intervals. The frequency band may be partitioned into three frequency subbands. Data may then be exchanged with users in first, second and third outer regions on first, second and third frequency subbands, respectively. The regions in which the users are located may be determined based on pilot and/or other measurements.

I. CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to ProvisionalApplication Ser. No. 60/652,518, entitled “FREQUENCY PLANNING SCHEME FORAN OFDM SYSTEM,” filed Feb. 11, 2005, assigned to the assignee hereof,and expressly incorporated herein by reference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for mitigating interference in a wirelesscommunication system.

II. Background

A wireless multiple-access communication system can concurrently supportcommunication for multiple terminals on the downlink and uplink. Thedownlink (or forward link) refers to the communication link from thebase stations to the terminals, and the uplink (or reverse link) refersto the communication link from the terminals to the base stations.Multiple terminals may simultaneously transmit data on the uplink and/orreceive data on the downlink. This may be achieved by multiplexing thedata transmissions on each link to be orthogonal to one another in time,frequency, and/or code domain. The orthogonality ensures that the datatransmission for each terminal minimally interferes with the datatransmissions for other terminals.

A multiple-access system typically has many cells, where the term “cell”can refer to a base station and/or its coverage area depending on thecontext in which the term is used. Data transmissions for terminals inthe same cell may be sent using orthogonal multiplexing to avoid“intra-cell” interference. However, data transmissions for terminals indifferent cells may not be orthogonalized, in which case each terminalwould observe “inter-cell” interference from other cells. The inter-cellinterference may significantly degrade performance for terminalsobserving high levels of interference.

To combat inter-cell interference, a system may employ a frequency reusescheme in which each cell uses only a portion of a frequency bandavailable for the system. For example, the system may employ a 7-cellreuse pattern and a frequency use factor of 1/7. In this system, thefrequency band is divided into seven frequency subbands, and each cellin a 7-cell cluster is assigned one of the seven frequency subbands.Each cell uses only one frequency subband, and every seventh cell reusesthe same frequency subband. With this frequency reuse scheme, the samefrequency subband is only reused in cells that are not adjacent to eachother, and the inter-cell interference observed in each cell is reducedrelative to the case in which all cells use the entire frequency band.However, a small frequency use factor (e.g., 1/7) represents inefficientuse of the available system resources since each cell is able to useonly a fraction of the frequency band.

There is therefore a need in the art for techniques to reduce inter-cellinterference in a more efficient manner.

SUMMARY

Techniques that can mitigate inter-cell interference in an efficientmanner are described herein. According to an embodiment of theinvention, an apparatus is described which includes at least oneprocessor and a memory. The processor(s) exchange data with (e.g., senddata to and/or receive data from) users in at least one inner region ofa cell in a first time interval on a frequency band. The processor(s)exchange data with users in multiple outer regions of the cell in asecond time interval on multiple frequency subbands formed with thefrequency band. For example, the frequency band may be partitioned intothree non-overlapping frequency subbands. The processor(s) may thenexchange data with users in first, second and third outer regions onfirst, second and third frequency subbands, respectively, in the secondtime interval. Adjacent outer regions in neighboring cells may usedifferent frequency subbands in the second time interval to mitigateinter-cell interference. The regions in which the users are located maybe determined based on pilot and/or other measurements.

According to another embodiment, a method is provided in which data isexchanged with users in at least one inner region of a cell in a firsttime interval on a frequency band. Data is exchanged with users inmultiple outer regions of the cell in a second time interval on multiplefrequency subbands formed with the frequency band.

According to yet another embodiment, an apparatus is described whichincludes means for exchanging data with users in at least one innerregion of a cell in a first time interval on a frequency band. Theapparatus further includes means for exchanging data with users inmultiple outer regions of the cell in a second time interval on multiplefrequency subbands formed with the frequency band.

According to yet another embodiment, an apparatus is described whichincludes at least one processor and a memory. The processor(s) exchangedata with users in a first region of a sector in a first time intervalon a frequency band. The processor(s) exchange data with users in asecond region of the sector in a second time interval on a frequencysubband, which is a portion of the frequency band. Adjacent sectors inneighboring cells may use different frequency subbands in the secondtime interval to mitigate inter-cell interference.

According to yet another embodiment, a method is provided in which datais exchanged with users in a first region of a sector in a first timeinterval on a frequency band. Data is exchanged with users in a secondregion of the sector in a second time interval on a frequency subband.

According to yet another embodiment, an apparatus is described whichincludes means for exchanging data with users in a first region of asector in a first time interval on a frequency band. The apparatusfurther includes means for exchanging data with users in a second regionof the sector in a second time interval on a frequency subband.

According to yet another embodiment, an apparatus is described whichincludes at least one processor and a memory. The processor(s) exchangedata with a first set of users in a first time interval based on a firstfrequency reuse scheme. The processor(s) exchange data with a second setof users in a second time interval based on a second frequency reusescheme.

According to yet another embodiment, a method is provided in which datais exchanged with a first set of users in a first time interval based ona first frequency reuse scheme. Data is exchanged with a second set ofusers in a second time interval based on a second frequency reusescheme.

According to yet another embodiment, an apparatus is described whichincludes means for exchanging data with a first set of users in a firsttime interval based on a first frequency reuse scheme. The apparatusfurther includes means for exchanging data with a second set of users ina second time interval based on a second frequency reuse scheme.

According to yet another embodiment, a terminal is described whichincludes at least one processor and a memory. The processor(s) exchangedata with a base station on a frequency band in a first time interval ifthe terminal is located in an inner region of a sector or a cell. Theprocessor(s) exchange data with the base station on a frequency subbandin a second time interval if the terminal is located in an outer regionof the sector or cell. The frequency subband is one of multiplefrequency subbands formed with the frequency band.

According to yet another embodiment, a method is provided in which datais exchanged with a base station on a frequency band in a first timeinterval if a terminal is located in an inner region of a sector or acell. Data is exchanged with the base station on a frequency subband ina second time interval if the terminal is located in an outer region ofthe sector or cell.

According to yet another embodiment, an apparatus is described whichincludes means for exchanging data with a base station on a frequencyband in a first time interval if a terminal is located in an innerregion. The apparatus further includes means for exchanging data withthe base station on a frequency subband in a second time interval if theterminal is located in an outer region of the sector or cell.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless multiple-access communication system.

FIG. 2 shows a model for an unsectorized cell.

FIG. 3 shows an exemplary cell layout for a cluster of sevenunsectorized cells.

FIGS. 4A and 4B show scheduling of users in inner and outer regions,respectively.

FIG. 5 shows a model for a sectorized cell.

FIG. 6 shows an exemplary cell layout for a cluster of seven sectorizedcells.

FIGS. 7A and 7B show two exemplary frequency subband structures.

FIG. 8 shows an exemplary transmission timeline.

FIG. 9 shows a process to transmit data in a cell.

FIG. 10 shows a process to transmit data in a sector.

FIG. 11 shows a process to transmit data with multiple frequency reuseschemes.

FIG. 12 shows a process to exchange data by a terminal.

FIG. 13 shows a block diagram of a base station and a terminal.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

FIG. 1 shows a wireless multiple-access communication system 100. System100 includes a number of base stations 110 that support communicationfor a number of terminals 120. A base station is generally a fixedstation that communicates with the terminals and may also be referred toas a Node B, an access point, or some other terminology. Terminals 120are typically dispersed throughout the system, and each terminal may befixed or mobile. A terminal may also be referred to as a user equipment(UE), a mobile station, a wireless communication device, or some otherterminology. A terminal may communicate with one or possibly multiplebase stations on the downlink and/or uplink at any given moment. Theterms “terminal” and “user” are used interchangeably in the descriptionbelow.

For a centralized architecture, a system controller 130 couples to thebase stations and provides coordination and control for these basestations. System controller 130 may also be referred to as a radionetwork controller (RNC), a base station controller (BSC), a mobileswitching center (MSC), or some other terminology. For a distributedarchitecture, the base stations may communicate with one another asneeded, e.g., to serve the terminals, to coordinate usage of systemresources, and so on.

To increase capacity, the coverage area of a base station may bepartitioned into multiple sectors. Each sector may be defined by adifferent antenna beam pattern. For example, the base station coveragearea may be partitioned into three sectors with three beam patterns thatpoint 120° from each other. Each sector may be served by a basetransceiver subsystem (BTS). For a sectorized cell, the base station forthat cell typically includes the BTSs for all sectors of that cell. Ingeneral, the term “sector” can refer to a BTS and/or its coverage area,depending on the context in which the term is used. For simplicity, inthe following description, the term “base station” is used genericallyfor both a fixed station that serves a cell as well as a fixed stationthat serves a sector.

For simplicity, FIG. 1 shows each terminal communicating with oneserving base station on the downlink and uplink. Each terminal mayobserve inter-cell interference from other base stations on the downlinkand may cause inter-cell interference to other terminals on the uplink.

The transmission techniques described herein may be used for variouscommunication systems such as a Code Division Multiple Access (CDMA)system, a Time Division Multiple Access (TDMA) system, a FrequencyDivision Multiple Access (FDMA) system, an Orthogonal Frequency DivisionMultiple Access (OFDMA) system, a Single-Carrier FDMA (SC-FDMA) system,and so on. A CDMA system may implement one or more radio accesstechnologies (RATs) such as Wideband-CDMA (W-CDMA), cdma2000, and so on.cdma2000 covers IS-2000, IS-856, and IS-95 standards. A TDMA system mayimplement a RAT such as Global System for Mobile Communications (GSM).These various RATs and standards are known in the art. An OFDMA systemtransmits modulation symbols in the frequency domain on orthogonalfrequency bins using orthogonal frequency division multiplexing (OFDM).An SC-FDMA system transmits modulation symbols in the time domain onorthogonal frequency bins. A system may also utilize a combination ofradio technologies such as, e.g., W-CDMA and OFDM.

For clarity, the transmission techniques are described below for asystem with multiple frequency bins, which may be obtained with OFDM,SC-FDMA, or some other modulation technique. OFDM and SC-FDMA partitionthe system bandwidth or frequency band into multiple (K) orthogonalfrequency bins, which are also referred to as tones, sub-carriers, bins,and so on. Each frequency bin is associated with a respectivesub-carrier that may be modulated with data.

In an aspect, joint time and frequency division is used to mitigateinter-cell interference. In an embodiment, the available frequency bandis partitioned into multiple non-overlapping frequency subbands. Thetransmission timeline is also partitioned into time intervals. Some ofthe time intervals are designated as T_(in) time intervals, and someother time intervals are designated as T_(out) time intervals. Themultiple frequency subbands may be used in different time intervals tomitigate inter-cell interference, as described below.

The transmission techniques described herein may be used for a systemwith sectorized cells as well as a system with unsectorized cells. Asectorized cell is a cell that is divided into multiple sectors. Anunsectorized cell is a cell that is not divided into sectors.

FIG. 2 shows a model for an unsectorized cell 210. In this model, thecoverage area of a base station is modeled by an ideal hexagon. Ingeneral, a base station coverage area may be of any size and shape andis typically dependent on various factors such as terrain, obstructions,and so on. The base station coverage area may or may not be a contiguousarea, and the cell edge may be quite complex.

The base station coverage area may be partitioned into multiple regions.A region may also be called a section, an area, a portion, and so on. Inthe embodiment shown in FIG. 2, the base station coverage area ispartitioned into four regions 220 a, 220 b, 220 c and 220 d that arelabeled as regions 0, 1, 2 and 3, respectively. Region 0 is an innerregion and includes the center area of the cell. Region 0 is modeledwith a circle in FIG. 2. The users within region 0 are referred to asinner users or inner circle users. Regions 1, 2 and 3 are outer regionsand include the outer area of the cell. Each outer region is modeled byone third of the ideal hexagon, albeit without the center area thatbelongs to inner region 0. The users within regions 1, 2 and 3 arereferred to as outer users or outer circle users.

In an embodiment, the available frequency band is partitioned into threefrequency subbands that are denoted as f₁, f₂ and f₃. Frequency subbandf₁ includes K₁ frequency bins, frequency subband f₂ includes K₂frequency bins, and frequency subband f₃ includes K₃ frequency bins,where K=K₁+K₂+K₃ and K is the total number of frequency bins in thefrequency band. The frequency band may be partitioned in variousmanners, as described below. The three frequency subbands may includethe same or different numbers of frequency bins.

FIG. 3 shows an exemplary cell layout 300 for a cluster of sevenunsectorized cells that are labeled as cells 1 through 7. Each cell ispartitioned into an inner region 0 and three outer regions 1, 2 and 3,as shown in FIG. 2. In an embodiment, the inner region 0 for each cellis assigned all three frequency subbands f₁, f₂ and f₃. The three outerregions 1, 2 and 3 for each cell are assigned frequency subbands f₁, f₂and f₃, respectively. Hence, outer region i, for iε{1, 2, 3}, isassigned frequency subband f_(i). The users in each region may beallocated frequency bins in the frequency subband(s) assigned to thatregion.

In the embodiment shown in FIG. 3, each outer region of a given cell isadjacent to two outer regions that are assigned different frequencysubbands in two neighboring cells. For example, outer region 1 of cell 1is adjacent to outer region 2 of cell 2 and outer region 3 of cell 7.Outer region 2 of cell 1 is adjacent to outer region 1 of cell 5 andouter region 3 of cell 6. Outer region 3 of cell 1 is adjacent to outerregion 2 of cell 3 and outer region 1 of cell 4. Each outer region ofeach cell is thus orthogonal in frequency to two adjacent outer regionsin two neighboring cells.

FIG. 4A illustrates an embodiment of scheduling the inner users. In thisembodiment, the inner users in all cells are scheduled during the T_(in)time intervals. All three frequency subbands f₁, f₂ and f₃ may be usedfor the scheduled inner users in each cell. The inner regions for allcells are shown with gray shading. As shown in FIG. 4A, the inner regionfor each cell is located some distance away from the inner regions inthe neighboring cells. Hence, even if the inner users in these cells areassigned the same frequency bins, the inner users in each cell mayobserve small amounts of inter-cell interference from the inner users inneighboring cells and may cause small amounts of interference to theinner users in the neighboring cells.

FIG. 4B illustrates an embodiment of scheduling the outer users. In thisembodiment, the outer users in all cells are scheduled during theT_(out) time intervals. Only the assigned frequency subband, which is afraction of the frequency band, is used for the scheduled users in eachouter region of each cell. In FIG. 4B, outer regions 1 for all cells areshown with gray shading, outer regions 2 for all cells are shown withhorizontal hashing, and outer regions 3 for all cells are shown withdiagonal hashing. As shown in FIG. 4B, adjacent outer regions inneighboring cells are assigned different frequency subbands. Hence, theouter users in each outer region of each cell do not observe inter-cellinterference from the outer users in adjacent outer regions ofneighboring cells. The outer regions assigned the same frequency subbandf_(i) are generally separated from one another by one outer region. Theusers in a given outer region i thus observe small amounts of inter-cellinterference from the users in outer region i of neighboring cells andcause small amounts of inter-cell interference to the users in outerregion i of the neighboring cells.

In another embodiment, some or all cells may exchange data with theinner users in the T_(out) time intervals on the entire frequency band,in the same manner as in the T_(in) time intervals, albeit with reducedtransmit power. This embodiment provides some flexibility, e.g., ifthere are no or very few outer users in a given cell. The use of reducedtransmit power ensures low interference, if any, to other transmissionsin neighbor cells.

FIG. 5 shows a model for a sectorized cell 510. In the embodiment shownin FIG. 5, the base station coverage area is partitioned into threesectors 520 a, 520 b and 520 c that are labeled as sectors 1, 2 and 3,respectively. For the model shown in FIG. 5, the base station coveragearea is modeled by an ideal hexagon, and each sector is modeled by onethird of the ideal hexagon. In an embodiment, each sector is partitionedinto an inner region 522 and an outer region 524. In this embodiment,the cell includes three inner regions and three outer regions for thethree sectors of the cell.

FIG. 6 shows an exemplary cell layout 600 for a cluster of sevensectorized cells that are labeled as cells 1 through 7. Each cell ispartitioned into three sectors 1, 2 and 3, and each sector ispartitioned into an inner region and an outer region, as shown in FIG.5. In an embodiment, the three sectors 1, 2 and 3 for each cell areassociated with frequency subbands f₁, f₂ and f₃, respectively. Eachsector of a given cell is adjacent to two sectors that are associatedwith different frequency subbands in two neighboring cells. For example,sector 1 of cell 1 is adjacent to sector 2 of cell 2 and sector 3 ofcell 7. Sector 2 of cell 1 is adjacent to sector 1 of cell 5 and sector3 of cell 6. Sector 3 of cell 1 is adjacent to sector 2 of cell 3 andsector 1 of cell 4.

In an embodiment, each sector may communicate with the inner users onall frequency subbands during the T_(in) time intervals. Each sector maycommunicate with the outer users on the associated frequency subbandduring the T_(out) time intervals. As shown in FIG. 6, adjacent sectorsin neighboring cells are associated with different frequency subbands.Hence, the outer users in each sector of each cell do not observeinter-cell interference from the outer users in the adjacent sectors inthe neighboring cells.

The total transmit power P_(max) available for transmission on a givenlink may be divided across the frequency subband(s) used fortransmission. During the T_(in) time intervals, all K frequency bins maybe used for the scheduled inner users in each cell for the embodimentshown in FIG. 3 or in each sector for the embodiment shown in FIG. 5.The transmit power P_(k) for each frequency bin k may be set as:$\begin{matrix}{P_{k} = {\frac{P_{\max}}{K}.}} & {{Eq}\quad(1)}\end{matrix}$

During the T_(out) time intervals, K_(i) frequency bins in frequencysubband f_(i) may be used for the scheduled users in outer region i orsector i of each cell. The transmit power P_(k,i) for each frequency bink in outer region i or sector i may be set as: $\begin{matrix}{P_{k,i} = {\frac{P_{\max}}{K_{i}}.}} & {{Eq}\quad(2)}\end{matrix}$

As shown in equations (1) and (2), the per-bin transmit power P_(k) forthe inner users during the T_(in) time intervals is lower than theper-bin transmit power P_(k) for the outer users during the T_(out) timeintervals. The lower per-bin transmit power P_(k) results in lessinter-cell interference among the inner users.

For both sectorized and unsectorized cells, the regions in which theusers are located may be ascertained in various manners. In anembodiment, the region in which a given user u is located is determinedbased on an “active set” maintained by/for user u. The active set maycontain all cells/sectors that are serving the user, all cells/sectorsthat are candidates for serving the user, cells/sectors that arestrongly received by the user, cells/sectors that strongly receive theuser, and so on. A cell/sector may be added to the active set, forexample, if the received pilot power for the cell/sector, as measured byuser u, exceeds an add threshold. Alternatively or additionally, acell/sector may be added to the active set if the received pilot powerfor user u, as measured at the cell/sector, exceeds the add threshold. Acell/sector may also be added to the active set in other manners.

Table 1 lists some possible active sets for a given user in cell 1 inFIG. 3. Each active set contains one or two cells. For each active set,Table 1 gives the region in which the user is deemed to be located andthe frequency subband(s) that may be used for the user. If the activeset contains only cell 1, then the user is deemed to be located in innerregion 0 since no other cells are strongly received by the user. If theactive set contains cell 1 and another cell y, then the user is deemedto be located in the outer region that borders neighbor cell y sincecell y is also strongly received by the user. TABLE 1 Active Set RegionFrequency Subband(s) (1) 0 f₁, f₂, f₃ (1, 2) 1 f₁ (1, 3) 2 f₃ (1, 4) 2f₃ (1, 5) 3 f₂ (1, 6) 3 f₂ (1, 7) 1 f₁

In another embodiment, the region in which a given user is located isdetermined based on a position estimate for the user. The position ofthe user may be estimated using various position determinationtechniques such as, for example, Global Positioning System (GPS),Advanced Forward Link Trilateration (A-FLT), and so on. The region inwhich the user is located may be determined based on the positionestimate and cell layout information.

Several embodiments for determining the region in which a given user islocated have been described. The region in which the user is located mayalso be determined in other manners and/or based on other measurementsbesides received pilot power. For example, strong cells/sectors may beidentified based on signal-to-noise ratios (SNRs), channel gains, and soon. In general, the region in which a user is located may be determinedbased on direct measurements and/or deduced based on relatedmeasurements, cell layout, and/or other information.

The K total frequency bins in the frequency band may be distributed tothe non-overlapping frequency subbands in various manners. The frequencysubbands are non-overlapping or orthogonal in that each frequency binbelongs in only one subband, if any.

FIG. 7A shows a frequency subband structure 700, which is an embodimentof partitioning the frequency band into three frequency subbands f₁, f₂and f₃. In this embodiment, the K total frequency bins are distributedto the three frequency subbands such that each subband containsapproximately K/3 bins that are uniformly distributed across the entirefrequency band. Frequency subband f₁ may contain frequency bins 1, 4, 7,and so on, frequency subband f₂ may contain frequency bins 2, 5, 8, andso on, and frequency subband f₃ may contain frequency bins 3, 6, 9, andso on.

FIG. 7B shows a frequency subband structure 710, which is anotherembodiment of partitioning the frequency band into three frequencysubbands f₁, f₂ and f₃. In this embodiment, the K total frequency binsare distributed to the three frequency subbands such that each subbandcontains approximately K/3 consecutive bins. Frequency subband f₁ maycontain frequency bins 1 through K/3, frequency subband f₂ may containfrequency bins K/3+1 through 2K/3, and frequency subband f₃ may containfrequency bins 2K/3+1 through K.

In general, each frequency subband may contain any number of frequencybins and any one of the K total frequency bins. To obtain frequencydiversity, each frequency subband may contain frequency bins taken fromacross the frequency band, e.g., as shown in FIG. 7A. To reduce pilotoverhead for channel estimation, each frequency subband may contain ablock of consecutive frequency bins, e.g., as shown in FIG. 7B.

The same or different frequency subband structures may be used for thedownlink and uplink. For example, subband structure 700 may be used forthe downlink, and subband structure 710 may be used for the uplink. Thefrequency subbands for each link may be static or may be configurable.Information indicating which frequency bins are included in eachfrequency subband may be known by the terminals a priori and/or may bebroadcast by the base stations.

FIG. 8 shows an exemplary transmission timeline 800 that may be used forthe transmission techniques described herein. In the embodiment shown inFIG. 8, the transmission timeline is partitioned into time intervalsthat are alternately designated as T_(in) and T_(out) interval spans.Each T_(in) time interval spans N_(in) frames, and each T_(out) timeinterval spans N_(out) frames, where in general N_(in)>1 and N_(out)>1.Each frame may span any time duration, e.g., 2, 5, 10, 20, 40 or 80milliseconds (ms).

In general, the T_(in) and T_(out) time intervals may be the same ordifferent durations. The T_(in) and T_(out) time intervals may havefixed durations, which may be selected based on expected datarequirements for the inner and outer regions. Alternatively, the T_(in)and T_(out) time intervals may have configurable durations, which may beselected based on actual data requirements for the inner and outerregions.

The transmission techniques may also be used with a single frequencysubband or a single carrier. For example, each T_(out) time interval maybe partitioned into smaller T₁, T₂ and T₃ time intervals. The users inouter region 1 for all cells may be scheduled for transmission on thesingle frequency subband in the T₁ time intervals, the users in outerregion 2 may be scheduled in the T₂ time intervals, and the users inouter region 3 may be scheduled in the T₃ time intervals.

FIG. 9 shows an embodiment of a process 900 to exchange data inaccordance with the transmission techniques described herein. Process900 may be performed by a cell. The region in which each user is locatedis determined, e.g., based on the active set for the user, measurementsmade by the user for different cells or sectors, measurements made bydifferent cells or sectors for the user, and so on (block 912). The cellmay be partitioned into at least one inner region and multiple outerregions. For example, the cell may be partitioned into (1) one innerregion and three outer regions that are served by a single base station,e.g., as shown in FIG. 2, or (2) three inner regions and three outerregions that are served by three BTSs, e.g., as shown in FIG. 5. Thecell may also be partitioned into fewer or more regions. Thepartitioning of a cell into multiple regions may be achieved physicallywith different antenna beam patterns or virtually based on measurementsand/or other information.

The users in the inner region(s) are scheduled for transmission inT_(in) time intervals (block 914). The users in the outer regions arescheduled for transmission in T_(out) time intervals (block 916). Datais exchanged with the scheduled users in the inner region(s) on theentire frequency band in the T_(in) time intervals (block 918). Data isexchanged with the scheduled users in the multiple outer regions ondifferent frequency subbands in the T_(out) time intervals (block 920).For example, if there are three outer regions 1, 2 and 3, then thefrequency band may be partitioned into three frequency subbands f₁, f₂and f₃. Data may then be exchanged on all three frequency subbands withthe scheduled users in the inner region(s). Data may be exchanged onfrequency subbands f₁, f₂ and f₃ with the scheduled users in outerregions 1, 2 and 3, respectively. In each time interval, the totaltransmit power may be distributed across all frequency bins availablefor transmission in that time interval. A data exchange may comprisesending data to a user on the downlink, receiving data from the user onthe uplink, or both.

FIG. 10 shows an embodiment of a process 1000 to exchange data inaccordance with the transmission techniques described herein. Process1000 may be performed by a sector in a sectorized cell. The region inwhich each user is located is determined (block 1012). The users in theinner region are scheduled for transmission in T_(in) time intervals(block 1014). The users in the outer region are scheduled fortransmission in T_(out) time intervals (block 1016). Data is exchangedwith the scheduled users in the inner region on the entire frequencyband in the T_(in) time intervals (block 1018). Data is exchanged withthe scheduled users in the outer region on a designated frequencysubband in the T_(out) time intervals (block 1020). The designatedfrequency subband is a portion of the frequency band and is orthogonalto the frequency subbands for adjacent sectors in neighboring cells.Alternatively or additionally, data may be exchanged with the scheduledusers in the outer region in a portion of each T_(out) time interval.

FIG. 11 shows an embodiment of a process 1100 to exchange data inaccordance with the transmission techniques described herein. Process1100 may be performed by a sector or a cell. The regions in which usersare located are determined (block 1112). Data is exchanged with a firstset of users in a first time interval based on a first frequency reusescheme (block 1114). Data is exchanged with a second set of users in asecond time interval based on a second frequency reuse scheme (block1116). The first set of users may be users located in an inner region ofthe sector or in at least one inner region of the cell. The second setof users may be users located in an outer region of the sector or inmultiple outer regions of the cell. The first frequency reuse scheme maybe associated with a frequency-use factor of one and may allow theentire frequency band to be used for transmission. The second frequencyreuse scheme may be associated with a frequency use factor of less thanone and may allocate different frequency subbands or different parts ofthe second time interval to different outer regions or differentsectors.

FIG. 12 shows an embodiment of a process 1200 to exchange data inaccordance with the techniques described herein. Process 1200 may beperformed by a terminal. The region in which the terminal is located isdetermined, e.g., based on measurements made by the terminal fordifferent base stations and/or measurements made by the base stationsfor the terminal (block 1212). A determination is then made whether theterminal is located in an inner region or an outer region. Data isexchanged with at least one base station in a first time interval on afrequency band if the terminal is located in an inner region (block1214). Data is exchanged with at least one base station in a second timeinterval on a frequency subband if the terminal is located in an outerregion (block 1216). The frequency subband is a portion of the frequencyband.

FIG. 13 shows a block diagram of an embodiment of base station 110 andterminal 120. For the downlink, at base station 110, a transmit (TX)data processor 1310 receives traffic data for the scheduled terminals,processes (e.g., encodes, interleaves, and symbol maps) the trafficdata, and provides data symbols. As used herein, a data symbol is amodulation symbol for data, a pilot symbol is a modulation symbol forpilot, a modulation symbol is a complex value for a point in a signalconstellation (e.g., for M-PSK or M-QAM), and pilot is data that isknown a priori by both the base station and the terminals.

A modulator 1312 performs modulation for OFDM, SC-FDMA, and/or othermodulation techniques supported by the system. For OFDM, modulator 1312may (1) map the data symbols to frequency bins assigned to the scheduledterminals, (2) map pilot symbols to frequency bins used for pilottransmission, (3) transform the data and pilot symbols to the timedomain with an IFFT, and (4) append a cyclic prefix to each OFDM symbol.For SC-FDMA, modulator 1312 may (1) transform the data and pilot symbolsto the frequency domain with an FFT, (2) map the FFT output to assignedfrequency bins, (3) map zero values to unassigned frequency bins, (4)transform the mapped values to the time domain with an IFFT, and (5)append a cyclic prefix to each SC-FDMA symbol. Modulator 1312 provides astream of transmissions symbols, which may be OFDM symbols or SC-FDMAsymbols. A transmitter unit (TMTR) 1314 processes (e.g., converts toanalog, filters, amplifies, and frequency upconverts) the transmissionsymbols and generates a downlink signal, which is transmitted via anantenna 1316.

At terminal 120, an antenna 1352 receives the downlink signal from basestation 110 and provides a received signal to a receiver unit (RCVR)1354. Receiver unit 1354 conditions (e.g., filters, amplifies, frequencydownconverts, and digitizes) the received signal and provides datasamples. A demodulator (Demod) 1356 performs demodulation in a mannercomplementary to the modulation performed by modulator 1312 at basestation 110 and provides symbol estimates. A receive (RX) data processor1358 processes (e.g., demaps, deinterleaves, and decodes) the symbolestimates and provides decoded data.

On the uplink, at terminal 120, traffic data is processed by a TX dataprocessor 1370, further processed by a modulator 1372, and conditionedby a transmitter unit 1374 to generate an uplink signal, which istransmitted via antenna 1352. At base station 110, the uplink signal isreceived by antenna 1316, conditioned by a receiver unit 1330, processedby a demodulator 1332, and further processed by an RX data processor1334.

Controllers/processors 1320 and 1360 direct the operation at basestation 110 and terminal 120, respectively. Controllers/processors 1320and 1360 may also perform various functions for the transmissiontechniques described herein. For example, controller/processor 1320 mayperform or supervise process 900 in FIG. 9, process 1000 in FIG. 10,and/or process 1100 in FIG. 11. Controller/processor 1360 may perform orsupervise process 1200 in FIG. 12. Memory units 1322 and 1362 store dataand program codes for base station 110 and terminal 120, respectively.

For the transmission techniques described herein, a scheduler for asector, a cell, multiple sectors, or multiple cells may determine theregion in which each user is located, determine the frequency subband(s)that may be used for each user, schedule users for data transmission,and allocate frequency bins or assign traffic channels from theapplicable frequency subband(s) to the scheduled users. Each sector orcell may provide each scheduled user with the assigned frequency bins ortraffic channel, e.g., via over-the-air signaling. Each sector or cellmay send data on the downlink to the terminal and/or receive data on theuplink from the terminal on the assigned frequency bins.

For clarity, the transmission techniques have been specificallydescribed for OFDM and SC-FDMA, with each frequency subband includingmultiple frequency bins formed with OFDM or SC-FDMA. The transmissiontechniques may also be used for other communication systems. Forexample, the techniques may be used for a CDMA system with threecarriers. A carrier may have a bandwidth of 1.23 MHz in cdma2000. Theinner region(s) of each cell may be assigned all three carriers, and thethree outer regions or sector of each cell may be assigned differentcarriers.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. An apparatus comprising: at least one processor configured toexchange data with users in at least one inner region of a cell in afirst time interval on a frequency band, and to exchange data with usersin multiple outer regions of the cell in a second time interval onmultiple frequency subbands formed with the frequency band; and a memorycoupled to the at least one processor.
 2. The apparatus of claim 1,wherein the at least one processor exchanges data with users in eachouter region on a different frequency subband that is non-overlappingwith at least one frequency subband used for at least one adjacent outerregion in at least one neighboring cell.
 3. The apparatus of claim 1,wherein the multiple outer regions comprise first, second and thirdouter regions, wherein the multiple frequency subbands comprise first,second and third frequency subbands, and wherein the at least oneprocessor exchanges data with users in the first, second and third outerregions on the first, second and third frequency subbands, respectively,in the second time interval.
 4. The apparatus of claim 1, wherein the atleast one processor exchanges data with at least one user in the atleast one inner region in the second time interval at reduced transmitpower.
 5. The apparatus of claim 1, wherein the at least one processordetermines regions in which users are located based on pilotmeasurements.
 6. The apparatus of claim 1, wherein the at least oneprocessor determines an active set for a user and determines a region inwhich the user is located based on the active set.
 7. The apparatus ofclaim 1, wherein the frequency band comprises a plurality of frequencybins, and wherein each of the multiple frequency subbands comprises adifferent subset of the plurality of frequency bins.
 8. The apparatus ofclaim 1, wherein the at least one processor exchanges data with theusers using orthogonal frequency division multiplexing (OFDM).
 9. Theapparatus of claim 1, wherein the at least one processor exchanges datawith the users using single-carrier frequency division multiple access(SC-FDMA).
 10. A method comprising: exchanging data with users in atleast one inner region of a cell in a first time interval on a frequencyband; and exchanging data with users in multiple outer regions of thecell in a second time interval on multiple frequency subbands formedwith the frequency band.
 11. The method of claim 10, wherein theexchanging data with the users in the multiple outer regions comprisesexchanging data with users in first, second and third outer regions onfirst, second and third frequency subbands, respectively, in the secondtime interval.
 12. The method of claim 10, further comprising:processing the data for the users in the at least one inner region andthe data for the users in the multiple outer regions with orthogonalfrequency division multiplexing (OFDM).
 13. The method of claim 10,further comprising: determining regions in which users are located basedon pilot measurements.
 14. An apparatus comprising: means for exchangingdata with users in at least one inner region of a cell in a first timeinterval on a frequency band; and means for exchanging data with usersin multiple outer regions of the cell in a second time interval onmultiple frequency subbands formed with the frequency band.
 15. Theapparatus of claim 14, wherein the means for exchanging data with theusers in the multiple outer regions comprises means for exchanging datawith users in first, second and third outer regions on first, second andthird frequency subbands, respectively, in the second time interval. 16.The apparatus of claim 14, further comprising: means for processing thedata for the users in the at least one inner region and the data for theusers in multiple outer regions with orthogonal frequency divisionmultiplexing (OFDM).
 17. The apparatus of claim 14, further comprising:means for determining regions in which users are located based on pilotmeasurements.
 18. An apparatus comprising: at least one processorconfigured to exchange data with users in a first region of a sector ina first time interval on a frequency band, and to exchange data withusers in a second region of the sector in a second time interval on afrequency subband corresponding to a portion of the frequency band; anda memory coupled to the at least one processor.
 19. The apparatus ofclaim 18, wherein the first and second regions are inner and outerregions, respectively, of the sector.
 20. The apparatus of claim 18,wherein the at least one processor distributes total transmit poweracross frequency bins in the frequency band for the first time interval,and distributes total transmit power across frequency bins in thefrequency subband for the second time interval.
 21. An apparatuscomprising: means for exchanging data with users in a first region of asector in a first time interval on a frequency band; and means forexchanging data with users in a second region of the sector in a secondtime interval on a frequency subband corresponding to a portion of thefrequency band.
 22. The apparatus of claim 21, further comprising: meansfor distributing total transmit power across frequency bins in thefrequency band for the first time interval, and means for distributingtotal transmit power across frequency bins in the frequency subband forthe second time interval.
 23. An apparatus comprising: at least oneprocessor configured to exchange data with a first set of users in afirst time interval based on a first frequency reuse scheme, and toexchange data with a second set of users in a second time interval basedon a second frequency reuse scheme; and a memory coupled to the at leastone processor.
 24. The apparatus of claim 23, wherein the firstfrequency reuse scheme is associated with a frequency use factor of one,and wherein the second frequency reuse scheme is associated with afrequency use factor of less than one.
 25. The apparatus of claim 23,wherein the at least one processor selects the first set of users fromamong users in an inner region of a sector or a cell, and sends data tothe selected users in the inner region on a frequency band in the firsttime interval.
 26. The apparatus of claim 23, wherein the at least oneprocessor selects the second set of users from among users in multipleouter regions of a cell, and sends data to the selected users in themultiple outer regions on different frequency subbands in the secondtime interval.
 27. The apparatus of claim 23, wherein the at least oneprocessor selects the second set of users from among users in multipleouter regions of a cell, and sends data to the selected users in themultiple outer regions in different parts of the second time interval.28. The apparatus of claim 23, wherein the at least one processorselects the second set of users from among users in an outer region of asector, and sends data to the selected users in the outer region on afrequency subband in the second time interval.
 29. An apparatuscomprising: means for exchanging data with a first set of users in afirst time interval based on a first frequency reuse scheme; and meansfor exchanging data with a second set of users in a second time intervalbased on a second frequency reuse scheme.
 30. The apparatus of claim 29,wherein the means for exchanging data with the second set of userscomprises means for selecting the second set of users from among usersin multiple outer regions of a cell, and means for exchanging data withthe selected users in the multiple outer regions on different frequencysubbands in the second time interval.
 31. The apparatus of claim 29,wherein the means for exchanging data with the second set of userscomprises means for selecting the second set of users from among usersin an outer region of a sector, and means for exchanging data with theselected users in the outer region on a frequency subband in the secondtime interval.
 32. A terminal comprising: at least one processorconfigured to exchange data with a base station on a frequency band in afirst time interval if the terminal is located in an inner region of asector or a cell, and to exchange data with the base station on afrequency subband in a second time interval if the terminal is locatedin an outer region of the sector or cell, the frequency subband beingone of multiple frequency subbands formed with the frequency band; and amemory coupled to the at least one processor.
 33. The terminal of claim32, wherein the at least one processor determines the region in whichthe terminal is located based on an active set for the terminal.
 34. Theterminal of claim 32, wherein the at least one processor obtains pilotmeasurements for base stations, and determines the region in which theterminal is located based on the pilot measurements.
 35. A methodcomprising: exchanging data with a base station on a frequency band in afirst time interval if a terminal is located in an inner region of asector or a cell; and exchanging data with the base station on afrequency subband in a second time interval if the terminal is locatedin an outer region of the sector or cell, the frequency subband beingone of multiple frequency subbands formed with the frequency band. 36.The method of claim 35, further comprising: obtaining pilot measurementsfor base stations, and determining the region in which the terminal islocated based on the pilot measurements.
 37. An apparatus comprising:means for exchanging data with a base station on a frequency band in afirst time interval if a terminal is located in an inner region of asector or a cell; and means for exchanging data with the base station ona frequency subband in a second time interval if the terminal is locatedin an outer region of the sector or cell, the frequency subband beingone of multiple frequency subbands formed with the frequency band. 38.The apparatus of claim 37, further comprising: means for obtaining pilotmeasurements for base stations, and means for determining the region inwhich the terminal is located based on the pilot measurements.